This invention relates to energy saving fluorescent lamp systems and, in particular, to a lamp system having a built-in protective device for preventing overcurrent in case one of the lamps of a two-lamp system fails to operate and to a fluorescent lamp structure therefor. In recent years, there has been interest in reducing the energy consumed by existing fluorescent lamp systems. A number of devices have been disclosed for accomplishing this purpose. One such device is disclosed in U.S. Pat. No. 3,954,316 dated May 4, 1976, issued to J. F. Luchetta. The Luchetta patent describes an attachment for inclusion in a two-lamp rapid-start-type fluorescent lamp. It comprises an isolation transformer and a capacitor to reduce the electrical power consumption of a lamp. A capacitor is placed in series with the existing power factor correcting capacitor in the standard rapid-start ballast and thereby reduces the current after energization. The isolation transformer provides heater current for one of the electrodes of one of the lamps and also functions to improve the power factor.
Another energy saving device is disclosed in U.S. Pat. No. 3,956,665 dated May 11, 1976, issued to J. A. Westphal. The Westphal patent discloses an energy saving device for replacing a fluorescent lamp in a two-lamp serially connected fluorescent fixture. Frequently, in order to save energy, every other set of two fluorescent lamps are disconnected with their ballast remaining in the circuit. The unloaded ballasts have an undesirable inductive power factor. The Westphal device permits the use of one of the two lamps by placing a capacitor in series with the lamp, thereby providing somewhat improved light distribution and power factor.
In U.S. Pat. No. 4,082,981 dated Apr. 4, 1978, issued to Morton et al. is disclosed an energy saving device for a rapid-start series-sequence type ballast for two low pressure mercury discharge lamps. The apparatus utilizes switch means in conjunction with a capacitor to limit the current supplied to the lamps after the lamps are energized.
In U.S. Pat. No. 4,163,176 dated July 31, 1979, issued to Cohen et al. is disclosed an instant-start fluorescent lamp and an elongated extension base housing a capacitance for reducing current flow through the lamp.
In U.S. Pat. No. 4,010,399 dated Mar. 1, 1977, issued to Bessone et al. is disclosed a switching circuit for a fluorescent lamp with heated filaments. The switching circuit may be held within one stem member cavity of the fluorescent lamp.